Book holder



FIG. 1 is a reduced perspective view of a book holder showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a right end elevational view thereof;

FIG. 4 is a side elevational view thereof;

FIG. 5 is a left end elevational view thereof; and

FIG. 6 is a bottom plan view. 

The ornamental design for a book holder, substantially as shown and described. 